On Tue, Feb 15, 2011 at 06:49:38PM +0100, Thomas Treutner wrote: > Hi, > > does somebody know what the following paragraph exactly means resp. > what it should mean? > > "The maximum bandwidth (in Mbps) that will be used to do migration > can be specified with the bandwidth parameter. *If set to 0, libvirt > will choose a suitable default*." In this case we choose to leave the default on whatever the QEMU default is. > http://libvirt.org/html/libvirt-libvirt.html#virDomainMigrate > > What is the "suitable default"? I looked through the code for qemu > and the only call to qemuMonitorSetMigrationSpeed() I can find is in > ./src/qemu/qemu_driver.c:8406, using libvirt 0.8.7. When I remember > correctly the second condition in a conjunction will not be > evaluated if the first one evaluates to false? So if resource == 0, > no limit will be set? > > I ask because I discovered that qemu is live migrating with a hard > coded throttle of 32MiB/s for historic reasons, which is an > activated handbrake if you have GBit Ethernet and additionally > annoying when thinking about qemu's broken way of live migration (no > maximum amount of iterations, no forced action, no error message, no > abortion - no *nothing*.). Effectively *using* GBit Ethernet often > solves this problem as the bandwidth to transfer dirty pages is > quadrupled. > > Also see qemu mailing list, Message-ID: <4D52D95D.3030300@xxxxxxxxxx> Yep, QEMU needs to remove that limit IMHO > > There was a short discussion on IRC where concerns of "breaking > libvirt" when deactivating the default limit were stated. If there > really are applications that depend on handbraked live migration, I > think these applications just should pass the limit they need to > virDomainMigrate(). What do you think? Yes, they should not be relying on any default, since the default is unspecified. Daniel -- |: http://berrange.com -o- http://www.flickr.com/photos/dberrange/ :| |: http://libvirt.org -o- http://virt-manager.org :| |: http://autobuild.org -o- http://search.cpan.org/~danberr/ :| |: http://entangle-photo.org -o- http://live.gnome.org/gtk-vnc :| -- libvir-list mailing list libvir-list@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/libvir-list